correctly restore zoom focus state after restart (from nick mainsbridge)
fix crash caused by trying to unregister null ports
add basic display of existing MIDI ports to audio/MIDI setup
remove JACK related menu items (audio/MIDI setup is where this happens now)
change return type on {disconnect_from,reconnect_to}_engine() and make public so that we can use these when doing intentional disconnects without popping up the "HALTED" dialog
remove JACK related action definitions (audio/MIDI setup is where this happens now)
substantive changes to allow the audio/MIDI setup dialog to change settings as intended

So far only tested with JACK backend, but expected to be more correct for other backends too
minor code changes
Merge branch 'master' into cairocanvas